There are 52 cards in a deck. Four kings and 13 clubs. So the probability of choosing a king or a club is 17/52. The probability that it's both a king and a club is 1/52 because it's only one king that's a club. Hence for drawing a card from a deck, each outcome has probability 1/52. The probability of an event is the sum of the probabilities of the outcomes in the event, hence the probability of drawing a spade is 13/52 = 1/4, and the probability of drawing a king is 4/52 = 1/13.
